1. Field of the Invention
The present invention relates to a rotary-type throttle valve carburetor for a spark ignition internal combustion engine. More particularly, the present invention provides an improved rotary valve carburetor which is designed primarily for use with engines of racing vehicles which function to immediately provide the required fuel upon the opening of the control throttle by the use of a rotary-body type throttle valve that significantly reduces or eliminates resistance on the throttle valve as a result of flow through the venturi of a carburetor.
2. Description of Related Prior Art
Internal combustion engines typically employ a butterfly valve in a throttle body assembly of a carburetor to control air intake. The carburetor mixes fuel with the air flow through the air intake to form a combustible fuel/air mixture. In today's mass produced motor vehicles, federal regulations mandate a minimum amount of exhaust emission pollutants and hence places a high demand on air/fuel mixture preparation if compliance with these regulations is to be achieved. Since carburetors of the butterfly valve type have limitations in fine tuning, response time, inertia, as well as size and weight restrictions, carburetors have been replaced by fuel injection systems because these systems lend themselves to more precise metering and therefore control of the air/fuel mixture over the complete operational range of the internal combustion engine. The use of fuel injection systems in passenger car vehicles has also been a major contributor to meeting the strict fuel economy standards that must be complied with as well as concerns with good idle quality.
The demands for higher horsepower engines for racing applications are an objective that runs completely opposite to the regulations mandated objectives for passenger car vehicles. Therefore, fuel delivery systems for racing applications are not subject to the mandated regulations for passenger car vehicles. As a result, carburetors for racing applications have been developed that do not use a butterfly throttle assembly to control the air intake. If one considers the operation of a prior art throttle plate assembly within the carburetor, it is readily understood why such configuration is unacceptable for applications where maximum horsepower is the only criteria.
For example, a prior art carburetor has a body having a throughbore defining a venturi. Air flows through the throughbore before entering the engine. A fuel line extends between a fuel reservoir and the venturi to deliver fuel from the fuel reservoir and mix the fuel with the air to form a combustible mixture. The throttle plate located in the throughbore, downstream of the venturi, opens and closes the throughbore to regulate the flow of the fuel/air mixture in response to the demand of the engine. As the throttle plate opens, airflow through the venturi increases. More fuel is mixed with the increasing airflow to maintain a combustible air/fuel mixture as the engine speed increases. Conversely, when the throttle plate closes, the airflow decreases and the amount of fuel mixed with the air decreases as engine speed decreases.
The venturi includes a reduced diameter throat. The speed of the air flow increases through the reduced diameter throat and its air pressure decreases by a physical effect known as the venturi effect. The reduced air pressure generates a partial vacuum or suction in the venturi throat. The fuel supply line opens in the venturi throat so that the suction draws fuel from the fuel reservoir through the fuel line and into the venturi to form the air/fuel mixture.
The amount of fuel mixed with the airflow is metered to form the optimum air/fuel mixture required for combustion. This ratio is referred to as the stoichiometric ratio. If too much fuel is added to the air flow, the air/fuel mixture is too rich. If not enough fuel is added, the air/fuel mixture is too lean. In either case the engine performance will suffer and engine power is reduced. In racing application, the optimum air/fuel mixture delivered by the carburetor should be maintained over the entire range of engine operation for best engine performance.
The problem with the above-described carburetor is that the throttle plate is located in the mainstream of the flow or air passing through the body of the carburetor. At full throttle operation, typical of most racing engine applications for 85%-95% of their lifespan, the airflow through the carburetor is so great that the airflow creates a drag on the throttle plate because it obstructs the flow of air through the carburetor. This friction acting on the throttle plate acts to reduce the momentum of the airflow resulting in turbulence destroying symmetries such that the overall result on the throttle plate interferes with acceleration, and maximum performance will suffer and engine power will be reduced. Further, presence of the throttle plate within the throat of the carburetor restricts the flow of air through the venturi than if there was no throttle plate to deal with. It is this problem that led to the development of the rotary valve carburetor.
Although rotary valve carburetors solve most of the problems created by the use of a throttle plate, the rotary valve carburetor has its own shortcomings. For passenger vehicle applications and the associated fuel economy and clean air restrictions, the rotary carburetor was an unfeasible choice because of the fuel management problems across the full range of vehicle operations. Significantly tighter tolerance requirements in manufacturing, to prevent leakage of fuel and proper fuel/air ratios over the entire range of engine operations, i.e., from idle to high speed applications, became cost prohibitive when compared to fuel injection fuel delivery systems. Therefore, butterfly valve or slide valve carburetor applications were limited to smaller engine applications such as snowmobiles, personal watercrafts, all-terrain vehicles and motorcycles as well as lawn mowers, chainsaws, and the like. However, increasingly strict gas emission regulations have made the applications to the latter more demanding and costly. However, for high performance racing application, these regulations and cost can be mitigated.
A further attempt to avoid the shortcomings of a butterfly valve carburetor resulted in the development of an aftermarket modification known as the flat slide throttle valve carburetor such as disclosed in U.S. Pat. No. 4,008,298 owned by the inventor of the present patent application.
The flatslide carburetor has a higher flow rate than a butterfly valve carburetor through the carburetor throat for a given pressure due to the lower frictional losses caused by the flat throttle plate. The lower losses are due to the relatively smaller surface area of the flat plate parallel to the direction of the airflow. Whereas the round side has an idealized frictional surface area equal to the area of the circular cross section of the barrel, the idealized frictional surface area of the flat slide carburetor is equal to the area of the flat plate edge times its width, which is typically a substantially lower value.
Further, the flat slide throttle plate occupies less volume in the carburetor throat and requires relatively less machining. In areas of the throat that contribute to flow restrictions and random localized turbulence. In practice, the flat slide carburetor increases the flowrate by approximately 15% at intermediate throttle settings and a percent or so at full throttle. These improvements in performance come at a relatively high price due to the higher manufacturing costs of the flat slide configuration.
All of the aforementioned devices suffer from frictional drag and discontinuities in the carburetor throat, caused either by the shape of the slide itself or by the machining within the carburetor throat required to accommodate the slide or butterfly throttle plate.
In light of the above, there is a continuing need for an improved rotary throttle valve type carburetor which will enable an internal combustion engine to secure the necessary amount of fuel during low-speed operation, such as during idling of the engine, and have an improved fuel delivery characteristic during acceleration and high-speed operation of the engine.